Hearing instruments that are positioned inside the ear typically include a means for controlling the sound pressure inside the ear by venting pressure inside the ear canal. Typically, a vent in the form of a canal extending through the hearing instrument from outside the ear to inside the ear is utilized to relieve pressure in the ear canal. Venting to permit pressure equalization and to reduce the occlusion effect caused by a completely sealed ear canal is a known technique.
A prior art hearing instrument is depicted in FIG. 1 installed in an ear canal. The hearing instrument includes a vent in the form of an elongated tube that extends from an inner surface of the hearing instrument, inside the ear, to an outer surface of the hearing instrument, outside the ear. The hearing instrument includes an opening on the outer surface that is coupled to a microphone for receiving sound signals from outside the ear. A receiver is coupled electronically to the microphone and reproduces sound signals to the ear canal through an opening on the inner surface of the hearing instrument.
In many hearing instruments, sound energy escapes from inside the ear canal through the vent and leaks back to the hearing instrument microphone, causing acoustic feedback. This is an undesirable characteristic.